The use of lengthy conduits for the purpose of transporting a fluid is common to many technical fields. Familiar examples include hydrocarbon production and transportation, water distribution, municiple sewerage, coal slurry pipelining, steam distribution, and pneumatic transfer systems. It is often necessary to pass tools through such conduits to perform maintenance, monitoring and other tasks. This is an especially common practice in hydrocarbon production and transportation, where it is often necessary to transport conduit cleaning elements, well logging equipment, various types of valves, impression block tools and other equipment through a pipeline, wellbore casing, service line or borehole.
One class of through-conduit tool used for this purpose is adapted to be pumped through the conduit to the desired location. The use of such tools requires that a fluid circulation path be present through the conduit. In another class of through-conduit tool, adapted for use in downwardly inclined conduits, positioning by gravity and retrieval by cable are utilized. However, if a fluid circulation path does not exist, or is blocked, and if gravity positioning is not possible, operations requiring the use of through-conduit tools pose substantial difficulties.
For use in situations where positioning by fluid circulation or gravity is not possible, several types of through-conduit propulsion devices have been developed. One such propulsion device is disclosed in U.S. Pat. No. 2,518,330, issued Aug. 8, 1950. This device includes two conduit gripping elements which may be extended and retracted relative to one another by a pneumatic element. The pneumatic element is powered by an external pneumatic pressure source connected by flexible hose to the propulsion device. One of the gripping elements anchors itself to the conduit upon extension of the gripping element and the other anchors itself upon retraction of the gripping element. In this manner, the pneumatic element moves in inch-worm fashion through the conduit. This device is disadvantageous in that no mechanism is provided for allowing reversal of the direction of travel. Further, the use of a pneumatic umbilical, owing to its relatively great diameter and significant weight per unit length, imposes a high drag on the propulsion device. Such an apparatus would be of little or no utility in conduits where there are many bends or where the distance to be travelled is great.
Another class of such propulsion devices receives fluid at one end and forceably ejects it from the other, in this manner propelling itself through the conduit. Examples of such devices are set forth in U.S. Pat. No. 4,378,051, issued Mar. 29, 1983 and U.S. Pat. No. 4,113,236, issued Sept. 12, 1978. Such devices are disadvantageous in that they must be connected by flexible cable to a remote power supply for powering the propulsion pump. The use of a flexible cable has many of the disadvantages of the hydraulic umbilical discussed above.
It would be advantageous to have a propulsion device for transporting equipment through a conduit wherein the propulsion device does not require the supply of electrical or fluid power transmitted through a cable or flowline extending through the conduit from an external power supply.